Here are some more keypoints we like to consider for our tanks (Armortek and others):
-- for outdoor activities 2 x 60 watts are a suggested minimum of power. A car hifi power amp (for subwoofers) with 250 watts is preferred, but most of them need only 12 volts and therefore a battery of its own or a voltage converter is necessary. A 24 V 250 W (or more) power amp would be a pretty good thing.
-- most sound modules have a 2-channel technology (for technical reasons). This needs also 2 loudspeakers to use the whole power. This is a little unhappy, because one big loudspeaker is much better in emitting deep frequencies than 2 smaller loudspeakers. Therefore I use one big loudspeaker with a double coil system which can fit 2 electrical channels in one chassis.
-- for realistic drive operation a tank model should run downhill not faster than uphill. Ok, this can also be achieved by drivers operation (reverse steering), but much easier to use is a built-in electronic brake system in the ESC; controllable by transmitter.
-- modern sound modules are much more powerful than simple SOUND producer; they control several functions like differentiated recoil (starting fast, slowing up at the end, reversing, moving back slowly), automatic track link squeaking depending on cornering, dedicated cold and warm start, random noises and many other features like radio messages and up to military songs for pauses in the fighting.........
-- all electronic components should be able to work with voltages up to 30 volts. Modern tank batteries (LiFePO4, LiYFePO4) will be charged up to this voltages, and when the user forgets to switch off the electronics when charging the battery they may be damaged.
Just my 2 cents...........